When a vehicle combination becomes unstable, this becomes noticeable in that the trailer is fishtailing. In this case, the trailer periodically transmits alternating forces via the trailer hitch onto the towing vehicle. These alternating forces lie essentially in the direction of the roadway perpendicular to the plane of travel. The frequencies of such trailer movements lie approximately between 0.5 Hz and 1.5 Hz.
German patent document no. 199 64 048 discusses a method and a device for stabilizing a road vehicle, in particular a passenger car having a trailer towed by the road vehicle. In this instance, the road vehicle is monitored with respect to fishtailing movements. When a fishtailing movement is detected, a yaw moment is automatically applied on the road vehicle, which is essentially in phase opposition to the fishtailing movement.
German patent document no. 100 41 093 discusses a sensor system and evaluation methods, which are suitable in a roller bearing for detecting physical quantities, particularly for detecting and evaluating quantities that are a function of rotational speed during the movement of the components supported in the roller bearing. The expansion forces caused by roller elements of the roller bearing and acting on the fixed bearing shell of the roller bearing are detected using expansion-sensitive sensors in that two sensors are attached on the bearing shell such that they are in each case offset with respect to each other by half of the angular distance of the roller elements in the direction of rotation. This invention is suitable for example for detecting braking, acceleration, lateral and vertical forces.